In a substrate processing apparatus that performs a film forming process on a substrate by a process such as atomic layer deposition (ALD) or the like, in order to instantaneously supply a reaction gas into a reaction vessel, a gas to be supplied is stored in advance in a buffer tank or the like and supplied into the reaction vessel by an injector such as a gas nozzle or the like while adjusting a flow rate with a mass flow controller (MFC) or the like.
For example, there is known a substrate processing apparatus which includes a reaction tube configured to accommodate and process a plurality of substrates, a gas nozzle for supplying a gas into the reaction tube, and an MFC for controlling a flow rate of a gas to be supplied, and performs a film forming process on the substrate by an ALD method.
In the conventional substrate processing apparatus, however, it takes a time to stabilize the flow rate and thus there may be a case where a sudden gas introduction occurs during that time. When the sudden gas introduction occurs before the gas flow rate becomes stable, there is a problem that quartz pieces cracked in the gas nozzle due to a byproduct adhered to the gas nozzle, delamination of a film formed in the gas nozzle and stress of the delaminated film, or the like are brought as particles (speck, dust or the like) into the reaction vessel, and these particles adhere to the substrate.
Furthermore, in order to prevent such particles from being brought into the reaction tube, conventionally, an operation of disassembling and cleaning a gas supply line including the injector of the substrate processing apparatus and reassembling the gas supply line is performed, but maintenance work is troublesome. In addition, although it is possible that a reaction gas is introduced into the gas nozzle to solidify a particle source (form a film) and thereby prevent the generation of particles, the gas holes of the gas nozzle or the like are blocked, making it impossible to perform the original gas supply.